[JellyBeanRacer]

After perusing around the internets for a while, attempting to discern which set of headphones would suit me, I've settled on these two pairs.
 
- Sennheiser HD 595
- Audio Technica ATH-M50
 
People from all over seem to be raving about the ATH-M50s, but at the same time the HD 595s, from what I've seen, are praised as some of the best-sounding headphones (for the price range) available.
 
I've heard the bit about the Sennheisers having terrible bass. Is there any validity to these statements? I'm currently using $7 Sony headphones and I find their bass levels satisfactory.
 
Is there anyone here who owns (or at least has recently tried) both? That would be most helpful.

I have never owned a pair of open-air headphones before. How bad is sound leakage? Is it like a cell phone ringtone, blaring computer speakers? I can't find any videos on the internet demonstrating sound leaking from the Sennheisers, and I am very disappointed in this fact.
 
Finally, which one sounds better and for what reasons? Pros and Cons for each?
 
Thanks guys.
 
- More Info: (1st Edit)
 
The type of music I listen to, in order of prominence: Symphonic Metal, New Age, Classical, Dubstep, Techno, Happy Hardcore, Death Metal.
 
(2nd Edit)
 
- I was thinking of powering whichever headphones I got with a FiiO E5. It seems like many people have had success with either set using these--and Amazon bundles them together. Comments on this? Would I need a better amp?

 

[hudamanium]

They're very different. It would be extremely difficult to get a good vote on which is better. You'll end up with people with different tastes in music and sound voting for the ones they own or their favorites. 
 
Either one of them is a great buy and will offer great sound. It just depends on what you're looking for. 
 
And leakage is significant on open headphones. If you're using them in libraries or in loud places do not get them. 

 

[Hayang]

I've had modded HD555s (identical to 595) and own the M50s.  They are both GREAT cans, but they shine at different things.  The HD595 will be warmer in mid lows and mids, and will have better soundstage.  The M50s have fuller bass, better isolation, and a very musical presentation that decreases the midrange a little, which has the effect of making pianos and vocals sound colder, but makes band mixes and such sound very coherent.

 

[JellyBeanRacer]

So, essentially, you all are saying that the difference in sound quality between the two sets is not different enough to be measurable? The difference doesn't matter?
 
Also, I'm not sure I understand "warm" and "cold" when used to describe sound. Would warm and cold kind of be like soft and hard, respectively?

 

[Digital-Pride]

Without getting too much into the technical details it really boils down to few things:
 
In the case of the Sennheisers you have a wider sound stage(meaning spatial placement of sounds and instruments think Dolby Digital surround sound), they have a pretty lively sound presention, somewhat forward musical signature.  Because of their open design, they produce a very nice clear airy sound.  They don't quite have the bass response of the M50s but it's there just not as emphasized.  Now the downside of the HD595's open design is they DO NOT block outside noise at all and they tend to leak sound even at moderate listening levels.  So if your planing on using them in noisy environments not a recommended 'phone.
 
 
In the case of the Audio-Technicas you get a nice bass signature that goes deep down with excellent musical texture and presentation.  They may not have as large a sound stage as the Sennheisers but you do get excellent instrument placement and spatial imaging.  The M50s have a foldable design for easy storage and portability.  And unlike the HD595s they noise isolate very well and don't leak out sound.
 
Both are excellent options and you really can't go wrong with either one.
 
Which one you say?  Well, since this is you first forray into the world of high quality audio I would recommend going with the M50s.  They're a great all around 'phone and an excellent entry into audiophile class headphones.

 

[Hayang]

I would say the two cans sound very different, but both are excellent in their own regard for the reasons listed above.
 
HD595 does not have "terrible" bass, but it is slightly underaccentuated.  M50s have ample bass and is slightly accentuated in that regard.
 
I think your main concern would be whether you want open or closed.  Think about this: With HD555/HD595 open headphones, if you are listening at 60% volume in a quiet bedroom, a person sitting 1 foot away from you will hear the music at about 10% volume.  A person 6 feet away would hear it at 4% or so.
 
Same situation, you listen at 40% volume.  1 foot away: 4%.  6 feet away: 2%.
 
It's not too bad, in my experience.  But it matters sometimes.  The other side of that is that you get great soundstage; the music will sound much more like it's coming from around you than from 2cm away from your ears.
 
I think open/closed is your main concern.  Once you get one I doubt you will be dissapointed with either set because they are both GREAT.